linux-kernel - Re: [PATCH] mm: fix long time stall from mm

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Message-ID: <20200211035004.GA242563@google.com>
Date:   Mon, 10 Feb 2020 19:50:04 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        Josef Bacik <josef@...icpanda.com>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: fix long time stall from mm_populate

On Mon, Feb 10, 2020 at 05:10:21PM -0800, Matthew Wilcox wrote:
> On Mon, Feb 10, 2020 at 04:19:58PM -0800, Minchan Kim wrote:
> >       filemap_fault
> >         find a page form page(PG_uptodate|PG_readahead|PG_writeback)
> 
> Uh ... That shouldn't be possible.

Please see shrink_page_list. Vmscan uses PG_reclaim to accelerate
page reclaim when the writeback is done so the page will have both
flags at the same time and the PG reclaim could be regarded as
PG_readahead in fault conext.

> 
>         /*
>          * Same bit is used for PG_readahead and PG_reclaim.
>          */
>         if (PageWriteback(page))
>                 return;
> 
>         ClearPageReadahead(page);
>